The present invention relates generally to fluid flow, and more particularly to a method and to a system for matching the fluid flow rate in two fluidly-unconnected flow paths.
Certain procedures require the matching of two fluid flow rates. Some conventional flow rate matching systems use a finely calibrated positive displacement pump (e.g., a peristaltic pump) in the first flow path and use a finely calibrated flow rate transducer in the second flow path. To match the flow rates, the pump speed of the finely calibrated (i.e., calibrated pump flow rate versus pump speed) positive displacement pump is controlled by using a pump speed corresponding to the calibrated pump flow rate which matches the flow rate reading of the finely calibrated flow rate transducer, as is understood by those skilled in the art.
What is needed is an improved method for matching first and second flow rates and an improved fluid flow-rate matching system useful, for example, in performing kidney dialysis.
A first method of the invention is for matching the flow rate of first and second fluid flows in respective, fluidly-unconnected first and second flow paths, wherein the first flow path includes a first flow source which includes a positive displacement pump having a controllable pump speed, and wherein the second flow path includes a second flow source and a flow-rate transducer. The first method includes steps a) through g). Step a) includes shutting off the second flow source. Step b) includes fluidly interconnecting the first and second flow paths creating an interconnected flow path which allows substantially the same flow from the positive displacement pump of the first flow source to encounter the flow-rate transducer. Step c) includes, after steps a) and b), obtaining readings from the flow-rate transducer for various values of the pump speed. Step d) includes, after step c), disconnecting the fluid interconnection between the first and second flow paths. Step e) includes turning on the second flow source. Step f) includes, after steps d) and e), obtaining a reading from the flow-rate transducer. Step g) includes controlling the flow rate of the first fluid flow to match the flow rate of the second fluid flow by controlling the pump speed using the value of the pump speed in step c) which corresponds to the reading of the flow-rate transducer in step c) which substantially matches the reading of the flow-rate transducer in step i.
In a first embodiment of the invention, a fluid flow-rate matching system includes a first fluid flow path, a second fluid flow path, a fluid interconnection path, and data. The first fluid flow path has in series a first flow source and a first valve, wherein the first flow source includes a positive displacement pump having a controllable pump speed. The second fluid flow path has in series a second valve and a flow-rate transducer. The fluid interconnection path has in series a first end, an interconnection valve, and a second end. The first end is in fluid communication with the first fluid flow path between the first valve and the positive displacement pump. The second end is in fluid communication with the second fluid flow path between the second valve and the flow-rate transducer. The data represent various values of the pump speed of the positive displacement pump and represent readings of the flow-rate transducer corresponding to the values of the pump speed taken with the first valve fully shut, the interconnection valve fully open, and the second valve fully shut. The pump speed is controlled from the reading of the flow-rate transducer taken with the first valve fully open, the interconnection valve fully shut, and the second valve fully open and from the data.
Several benefits and advantages are derived from one or more of the method and the embodiment of the invention. The matching of one fluid flow rate to another fluid flow rate, such as matching the flow rate of the replacement water stream to the flow rate of the waste water stream in kidney dialysis, is accomplished without having to use a calibrated positive displacement pump and a calibrated flow-rate transducer. Using an uncalibrated positive displacement pump and an uncalibrated flow-rate transducer reduces costs.